A coned disc spring has a body in a disc shape (approximately conical shape), and the body has a ring shape with a hole at the center. The coned disc spring can be used in various applications, such as, as a pressing means, a shock absorbing means, etc., in fields such as vehicles, industrial machines, consumer electrical appliances, etc. For example, in a converter (a converter and an inverter) for hybrid automobiles or electric automobiles, the coned disc spring is used as a pressing means for pressing semiconductor elements to a heat sink. In a driving device for vehicles, the coned disc spring is used as a shock absorbing means during a clutch engagement in a clutch mechanism (for example, see the following Patent Document 1).
Patent Document 1 is Japanese Unexamined Utility Application Publication No. 4-38127. Patent Document 2 is Japanese Patent No. 4065178.
However, when the coned disc spring is used as a pressing means for a semiconductor element, in the converter, in general, plural semiconductor elements are linearly arranged, and therefore, the pressing means is installed in a rectangular installation space. However, in the case in which one coned disc spring 1 is used, for example, as shown in FIG. 7A, it is necessary to correspond the outer diameter of the circular coned disc spring 1 to short sides of the rectangle of the installation space S. In this case, on long sides of the rectangle of the installation space S, dead space, which cannot be pressed by the coned disc spring 1, is formed. As a result, since one coned disc spring 1 must be installed on each semiconductor element, plural coned disc springs 1 are required, for example, as shown in FIG. 7B. Therefore, the number of parts and production cost are increased.
Accordingly, it is considered that a leaf spring having a shape corresponding to the rectangular installation space should be used. However, load characteristics of the leaf spring are different from load characteristics of an elliptical coned disc spring having non-linear characteristics, as shown in FIG. 8A, and has linear characteristics, as shown in FIG. 8B. As a result, the generated load varies greatly, even if the height of each of the semiconductor elements is slightly changed by height dispersion and thermal expansion between the semiconductor elements. Therefore, in order to reduce the number of parts and production cost and obtain the non-linear load characteristics, it is considered that an outer circumference of a coned disc spring should be an ellipse.
On the other hand, in the Patent Documents 1 and 2 in which a coned disc spring is used as a shock absorbing means for a clutch mechanism, it is proposed that the outer circumference of the body have an elliptical shape. For example, in the Patent Document 2, a coned disc spring is used as a shock absorbing means for a clutch mechanism, and in order to improve assembly of the coned disc spring to the clutch mechanism, the body and the hole of the coned disc spring are formed to have an elliptical shape. In this case, all plate widths of the bodies of the coned disc springs are set to be equal. In the clutch mechanism, an annular groove part is provided on a surface facing a friction plate side of a piston, and an inner circumference part of the hole of the coned disc spring is engaged with the annular groove part. However, in the elliptical coned disc spring, stress of a bending part at a long radial part side on the outer circumference is greater than that of a bending part at a short radial part side, and it is necessary to consider the stress of the bending part at the long radial part side in design. As a result, the design is limited. Here, in the present invention, the bending part at the long radial part side is a part at a long radial part side having a small radius of curvature and is a part within a range of a given angle from a long axis of an elliptical outer circumference, and the bending part at the short radial part side is a part at a short radial part side having a radius of greater curvature than that of the bending part at the long radial part side and is a part except for the bending part at the long radial part side on the elliptical outer circumference.